Seagliders in Puget Sound
They are sometimes called Autonomous Underwater Vehicles (AUVs), or submersible drones. They glide like airships through the deeper channels of Puget Sound, and have become an important tool for a wide array of open ocean applications, including detection of marine mammals, military reconnaissance and the monitoring of environmental disasters like the Deepwater Horizon oil spill. Puget Sound is the birthplace and key testing area of the Seaglider.
On a cool, foggy morning at Kayak Point State Park near Marysville, three chartreuse torpedo-like devices, each nearly two meters long stand propped up on the grass. Drawn in by the unusual sight, four gentlemen wander over from the parking lot. One of the curious onlookers gets right to the point. “What the heck are those?” he asks.
It's a familiar question to Corey Macdonald, who is standing nearby. “These things always attract attention,” he says. "We can’t go a day in the field without someone coming up and wanting to know if they are a weapon.”
The Seaglider has a multitude of uses— some of them indeed classified by the Defense Department (including "tactical oceanography" and "maritime reconnaissance")— but the talk today is of scientific readings, and Macdonald is here to help train sales staff and others in some of the finer points of Seaglider operations. Macdonald is the logistics manager for a company called iRobot, one of the manufacturers of the Seaglider, and right now, two trainees are under a picnic shelter, hunched over laptops. They type out commands—check to see whether the gliders get them—peck out more commands—all in preparation for a launch in Puget Sound.
A lot of Seaglider testing occurs in north Puget Sound’s deeper waters, where “there isn’t a lot of boat traffic, so we don’t have to worry about them getting run over,” says Macdonald. As a result, Seagliders have been regularly gathering datasets on that area for years, measuring among other things conductivity, temperature, depth (CTD)—the standard suite of metrics used when sampling the upper ocean.
The Seaglider was first developed in the 1990s by a team led by Charles Eriksen, a professor of oceanography at the University of Washington, as part of a joint effort between the School of Oceanography (now part of the College of the Environment) and the Applied Physics Laboratory (APL). “There was a real need for a long-range autonomous underwater vehicle,” says Fritz Stahr, the manager of the Seaglider Fabrication Center at the University of Washington, which eventually arose out of those early efforts.
The project received the bulk of its funding from the Office of Naval Research (ONR). For his part, Stahr started working with Seagliders in 2005 to fulfill an ONR directive that there be a quasi-commercial entity within the university that would bring manufacture of the Seagliders to a point where the commercial license could be sold. In 2008, iRobot won the license. The Fabrication Center now makes Seagliders for internal customers; iRobot, a military contractor based in Massachussets, makes them for everyone else.
How they work
The Seaglider is hydrodynamic, with two pairs of fins near the rear. These fins help the Seaglider “fly” underwater, as it were, using changes in buoyancy as thrust. It cannot go very fast (~0.5 knots), but it can travel about 20 km per day, and dive as deep as 1000 meters. Weighing just over 50 kilograms, it is “robust enough to handle the elements, but small enough that two people can pick it up,” says Macdonald.
The bulk of Seaglider research is done in the open ocean, where scientists have recognized the value of using gliders in rough weather and conditions that make surface monitoring treacherous, but make little difference under the water.
Deployments are organized as missions. A pilot first sends commands to the device, sometimes remotely—travel to this point, spend so much time at this depth—and once the commands are confirmed, the Seaglider is launched from a boat. When the first set of commands has been carried out, the Seaglider returns to the surface. It tilts over on its nose, raises its long antenna out of the water, and sends whatever data it collected back to the pilot via satellite, receives new instructions, and heads off again.
What the Seaglider lacks in pace it makes up in endurance. Depending on the size of its battery, it can deploy for months at a time. The longest such deployment, in the Labrador Sea, lasted seven months and covered 3,750 kilometers.
“They can handle rough seas, most strong currents,” Stahr says. “Basically, almost whatever we throw at them.”
Monitoring efforts
The Seaglider can operate both as a long-term monitoring capacity and also a responder. In the immediate aftermath of the Deepwater Horizon oil spill, for example, Macdonald himself went to Louisiana to help deploy an iRobot Seaglider in the Gulf of Mexico. (The U.S. Navy also deployed two of its own gliders.) “We aren’t scientists,” Macdonald says. “We just provided the data, and the let the scientists figure out what it all meant.”
The mission lasted 70 days. Although nothing was allowed within three kilometers of the well site, the Seaglider was able to survey waters about five kilometers away; the data were made publicly available and were part of the reason that the massive undersea plume of oil was detected. “The point of those were to look for the underwater oil plume we were told didn’t exist,” Stahr says. “Unfortunately, the gliders couldn’t get deep enough to find the bottom of it.”
Stahr thinks that such an application probably isn’t necessary for Puget Sound. The reason is the Sound is highly stratified. “The Macando Well was a venting event—oil pouring up from the bottom,” Stahr says. Since the region lacks oil deposits of that magnitude, to say nothing of the drilling operations, any oil spilled will likely occur at the surface. There, it combines with freshwater, which inhibits deep mixing.
Seagliders have continued to evolve, with increases in endurance (thanks to smaller batteries) and dive capacity. “There have been a lot of big changes since I came on,” says Stahr. “Charles Eriksen is working on a Deepglider that can go to 6,000 meters.” Surveys are also carried out under pack ice. One other recent application is marine mammal monitoring. (“Something the Navy is really interested in,” Stahr says.) Neil Bogue, with the Applied Seaglider Group at the University of Washington, uses Seagliders to track toothed whales—deep-diving cetaceans whose habits have previously proved difficult to study.
“The Seagliders are great listening platforms,” Stahr says. “They can actually get to the sound channel where the whales are vocalizing, and make confirmed sightings.” He catches himself. “Listenings is probably more accurate.”
A variety of AUVs
Other types of underwater gliders using similar technologies include the Spray glider developed at the Scripps Institution of Oceanography, and the Slocum, conceived in the late 1980s by Douglas C. Webb and further developed at the Woods Hole Oceanographic Institution. AUVs have also expanded to include surface wave gliders and the so-called "Gulper" which can collect water samples as it goes.
